High speed motorized spindles were initially developed for precision grinding and over the years have been used for other machining operations involving heavy stock removal such as rotary milling, end milling and end facing. In such spindles, the tool is diectly driven by the rotor of a high frequency, alternating current induction motor with no intervening belts, pulleys or the like to achieve rotational speeds up to 150,000 rpm. The rotor is typically supported in a housing by precision bearings which are axially preloaded to maintain rotor play and vibration within acceptable limits and to accommodate thermal strains generated in the system during operation. Typical prior art high speed spindle constructions including spring preloaded bearings are illustrated in the Moore U.S. Pat. No. 2,502,874 issued Apr. 4, 1950, the Arms U.S. Pat. No. 2,523,983 issued Sept. 26, 1950, the Bryant et al U.S. Pat. No. 2,550,908 issued May 1, 1951 and the Grobey U.S. Pat. No. 2,819,127 issued Jan. 7, 1958, all of common assignee herewith.
A recent improvement in high speed motorized spindle construction including an improved antifriction bearing support and an oil-mist lubrication system is illustrated in the Mitchell and Clark U.S. Pat. No. 4,211,454 issued July 8, 1980 of common assignee herewith. The Mitchell and Thayer U.S. Pat. No. 3,939,944 issued Feb. 24, 1976 also of common assignee herewith provides an oil mist lubrication system for the antifriction bearings of a high speed motorized spindle and an oil-mist blender-distributor unit.
Machine tools having hydraulic mechanisms for preloading high speed spindle bearings are disclosed in the McCann U.S. Pat. No. 3,211,060 issued Oct. 12, 1965 and the Bone U.S. Pat. No. 3,222,991 issued Dec. 14, 1965. In each patent, piston/cylinder assemblies located internally in the spindle construction engage the outer race of the rear spindle bearing to exert a preload on the front and rear bearings. In the McCann patent, the bearing preload is apparently maintained during machining by a motor-driven pump while in the Bone patent a hydraulically expandable sleeve attached to the piston member locks the member in the desired reload position.
The Jones U.S. Pat. No. 3,540,346 issued Nov. 17, 1970 discloses an annular biasing piston member engaging the outer race of a rear spindle bearing to axially preload the front and rear spindle bearings in a machine tool. The spindle is axially adjustable in a rotary sleeve and is clamped in desired axial position in the sleeve by a hydraulically actuated clamping bushing carried by the rotary sleeve.
Multiple piston/cylinder assemblies for varying loading on split-spindle bearings of a motorized spindle and for providing an end thrust on the spindle are disclosed in the Erikson et al U.S. Pat. No. 2,618,517 issued Nov. 18, 1952. Loading of the split bearings is achieved by radially oriented cylinder/piston assemblies and is employed to vary the thickness of the oil film between the bearings as a means to control spindle wobble. End thrust is applied to the spindle in a direction toward the cantilevered spindle end carrying the tool by multiple cylinder/piston assemblies oriented axially in an end collar.
Hydraulic clamping mechanisms for accurately positioning a machine tool spindle are disclosed in the Dever et al U.S. Pat. No. 3,244,028 issued Apr. 5, 1966, the Kampmeier U.S. Pat. No. 3,438,289 issued Apr. 15, 1969 and the Lehmukuhl U.S. Pat. No. 3,545,335 issued Dec. 8, 1970.
High speed motorized spindles adapted specifically for use with a conventional machining center having an automatic tool changer mechanism are disclosed in the Allgeyer U.S. Pat. No. 3,803,981 issued Apr. 16, 1974 and the Hutchins U.S. Pat. No. 4,077,736 issued Mar. 7, 1978.